1. Field of the Invention
The present invention relates to a circuit arrangement nearest for routine testing of the interface comprising an interface circuit and located between the line terminator groups of pairs of line terminator groups for the connection of telecommunication lines to the switching center of a pulse-code modulated (PCM) switching system and to the switching matrix network system, and in which the pairs of line terminator groups form a unit in such a fashion that, given outage of central parts of one of the line terminator groups, the telecommunication traffic appertaining to the total of telecommunication lines connected to this particular line terminator group can be sequenced via redundant parts of the other line terminator group in an alternate routing mode, to which end the interface circuits contain switch-over devices that, in the alternate routing mode, forward telecommunication information coming from the switching matrix network and intended for the line terminator group to which they are allocated not to the line terminator group, but to the redundant central parts of the other line terminator group or, respectively, conduct telecommunication information coming from the redundant central parts of this line terminator group to the switching matrix network terminals allocated to the other line terminator group. The present invention is accordingly related to a circuit configuration wherein line terminator groups for the connection of telecommunication lines to the switching center of a PCM telecommunication system form a unit in pairs in such a fashion that they can substitute for one another given outages at their central region.
2. Description of the Prior Art
As shown in FIG. 1, line terminator groups LTG to which links PCM30 are connected in the illustrated case form pairs of line groups LTGx1, LTGy1 - - - LTGxn, LTGyn. As critical components parts of these line terminator groups, interfaces DIUx, DIUy at the link side, as well as interface units LIUx, LIXy at the side of the switching matrix network SNO/SN1 are illustrated and group couplers GSx and GSy are shown as simple parts. The group couplers GS and the interface units LIU are redundant, whereby, as shown in FIG. 1, the one half is related to the sequencing of the telecommunication traffic in conjunction with the link connected to the appertaining line terminator group and the other half is related to the links connected to the partner line terminator group. The control-oriented connection of the line terminator groups is such that, during normal operation, the traffic in conjunction with the link connected to the one line terminator group is sequenced via the one half of the group coupler GS and via the interface circuit LIU and connections that relate to the link connected to the partner line terminator group are set up as a precautionary measure in the other half of the group coupler but are not connected through. The appertaining switching traffic is sequenced via the corresponding, redundant parts GS and LIU of the partner line terminator group only given an outage of the group coupler GS of a line terminator group LTG or of the interface unit LIU.
Belonging to the interfaces between the line terminator groups LTGx and LTGy are interface circuits SDCA that, among other things, contain switch-over devices that, in the equivalent circuit diagram, forward telecommunication information coming from the switching matrix network SN and destined for the line terminator group to which they are allocated, not to the line terminator group, but to the redundant central parts of the other line terminator group or, respectively, conduct telecommunication data coming from the redundant central parts of this, central line terminator group to the switching matrix network terminals allocated to this other line terminator group.
As indicated with broken lines, for connection between the line terminator groups and the second half SN1 of the redundant switching matrix network SN0/SN1, a respective second such interface circuit SDCA is provided for a pair of line terminator groups, i.e. a total of four interface circuits.
The present invention is therefore directed to the routine testing of the interfaces, i.e. of the connecting paths to the interface circuits SDCA and of the interface circuits themselves.
In this context of this time channels available for the transmission between the line terminator groups of and the switching matrix network (there being 128 time channels in a specific embodiment), a check code word was heretofore transmitted from the active line terminator group in normal operation with reference to the interface, was mirrored in the interface circuit and returned to the line terminator group for a comparison with the pattern of the transmitted check word occurred. The conditions during one time channel are therefore interpreted as representative of those during the other time channels. The parts of the interface that are in communication with the line terminator group that is passive during normal operation as well as the switch-over device within the interface circuit SDCA are not covered at all in this procedure.
This is disadvantageous insofar as it is not certain, in the case of the necessity of a switching into the standby mode, whether the appertaining interface parts or, respectively, the switch-over device can work properly.
Although it can be largely assured in the initially-mentioned alternate procedure that connection losses remain low when switching, a switching only for the purpose of implementing the routine tests in the aforementioned manner would lead to unreasonable deteriorations, since it must occur relative often. Moreover, the previous testing is also considered inadequate because of the aforementioned spot check character.